William Wrigley Jr. was raised in Philadelphia, where he was expelled from grammar school and worked for many years in his family soap-making business, the Wrigley Manufacturing Company. When his father allowed him a hand in running the company, he began offering baking soda as a premium to boost soap sales. When more customers asked for baking soda than Wrigley's Scouring Soap, he went into the baking soda business in 1891, leaving his father's employ, moving to Chicago, and borrowing $500 from his uncle to establish the William Wrigley Jr. Company. He offered chewing gum as a premium to help sell baking soda, and soon, again, more people wanted the premium than the product Wrigley was selling. Within months he abandoned baking soda and took his company into the chewing gum business.

Wrigley's first two gums, long forgotten now, were Lotta Gum for children and men, and Vassar brand gum for women. Wrigley's Spearmint was introduced in 1893, Juicy Fruit in 1894, and Doublemint "double strength" gum in 1914. Through shrewd use of advertising and the placement of Wrigley displays beside stores' cash registers, Wrigley's company came to dominate the chewing gum business, and from the sale of nickel packs of gum he became one of America's richest men. He purchased a share of the Chicago Cubs in 1916, bought majority control of the team in 1921, and renamed the team's ball park Wrigley Field in 1926. In 1919 he bought California's Catalina Island, turning it into a resort. He expanded his gum empire into Canada in 1910, Australia in 1915, and England in 1927. In 1920 the company began construction of the landmark Wrigley Building office tower in downtown Chicago, and his company is still headquartered there.

Through his entire life, Wrigley often stated his belief that there should be no comma between his last name and the "Junior". His son, Philip Knight Wrigley, served as President of Wrigley and the Cubs, and founded the All-American Girls Professional Baseball League.